1. Field of the Invention
The present invention relates to a system and method for controlling a variable displacement engine to manage temperature of a catalyst system.
2. Background Art
Fuel economy for a multi-cylinder internal combustion engine can be improved by deactivating some of the engine cylinders under certain operating conditions. Reducing the number of operating cylinders reduces the effective displacement of the engine such that it is sometimes referred to as a variable displacement engine. Depending upon the particular configuration of the variable displacement engine, one or more cylinders may be selectively deactivated to improve fuel economy under light load conditions. In some configurations, a group of cylinders, which may be an entire bank of cylinders, is selectively deactivated.
Reducing the number of operating cylinders may also reduce the operating temperature of various engine and/or vehicle components which may adversely affect desired engine operation. For example, certain emission control devices, such as catalytic converters, require a minimum operating temperature for efficient operation. One approach to raise catalyst temperature involves enriching the fuel supply to the operating cylinders when catalyst temperature drops below a specified level as disclosed in U.S. Pat. No. 4,467,602. This method assumes that excess air is available in the catalytic converter to be effective. The inventors herein have recognized that this assumption may not always be valid and may result in reduced catalyst and/or engine efficiency during certain operating conditions.
An object of the present invention is to provide a system and method for controlling a variable displacement internal combustion engine to effectively manage the temperature of one or more engine and/or vehicle components.
In carrying out the above object and other objects, advantages, and features of the invention, a system and method for controlling a variable displacement internal combustion engine include controlling the number or ratio of active/inactive cylinders to control the temperature of at least one engine or vehicle component. In one preferred embodiment, the system and method include controlling a variable displacement engine having a bank configuration with a close-coupled catalyst associated with each bank of cylinders and at least one downstream or underbody catalyst by activating the second bank of cylinders when one of the catalysts is determined to be near or below a minimum efficient operating temperature.
The present invention provides a number of advantages. For example, the present invention manages the temperature of one or more engine/vehicle components to maintain a desired operating efficiency while also efficiently operating the engine.
The above advantage and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.